ESA Astrobiology Topical Team Publications

Planet Earth and Space: Precious and sometimes unexpected tools for astrobiology research

In 1953, Stanley Miller performed an experiment seen as a turning point in the study of the origins of life on Earth: he demonstrated that key molecules considered essential for the appearance of life, namely amino acids,
can be "simply" formed in the atmosphere of a planet if it has the right initial ingredients: the appropriate molecules, the right conditions.
This historical experiment became a foundational element of what was called "exobiology" in 1960: an interdisciplinary field with the goal of understanding the origins of life on Earth and, by extension, knowing how and where to look for signs of extraterrestrial life.
Today, this discipline is broadly termed astrobiology. Many studies have provided a wealth of results over the past five decades, giving this scientific field in an important place in many academic research programs even as it became a priority for space agencies worldwide.
Understanding how life appears and finding its evidence elsewhere have become central questions in science, no longer relegated to science fiction.
Several years ago, the European Space Agency, ESA, brought together an international, interdisciplinary team of researchers, the "Astrobiology Topical Team".
Its charge was to review and report on the latest advances in the field in order to plan more strategically for the future. The work of these researchers is now published in a series of three scientific articles in a special issue of the journal Space Science Reviews
(volume 209).

Astrobiology and the possibility of life on Earth and elsewhere...

In its first article, the Topical Team addresses the latest advances in the broad, interdisciplinary field of astrobiology.
It is now known that the ingredients necessary for the appearance of life, including amino acids and many other organic molecules, can be found in meteorites that fall to Earth, and as an even larger relative constituent of comets.
From these elementary building blocks, chemists are elaborating new reasoning based on complex chemical systems that lead us to imagine how molecules such as RNA or proteins could have formed, leading to the emergence of life.
The turn of the decade beginning in 2010 has been particularly rich thus far in discoveries in this area, known as prebiotic chemistry.
In addition, recently developed scenarios for the formation of the planets of the Solar System have reshaped our understanding of the face of primitive Earth: our planet may have been inhabitable and inhabited much earlier than imagined as recently as the early 2000s.
Indeed, more and more indicators of life, in the form of microfossils or life-indicative chemical imbalances, have been found in the oldest rocks of our planet.
Terrestrial life, taken as reference, also demonstrates an astonishing ability to adapt to environments formerly considered too extreme to harbor life, broadening the perspective of finding life elsewhere in the Solar System.
Much further away, around other stars, thousands of recently-discovered exoplanets will soon be sufficiently well characterized using powerful telescopes to fuel our hopes of detecting signs of life outside our Solar System.
All these developments are detailed in an article "Astrobiology and the Possibility of Life on Earth and Elsewhere ..." (available online).

Tag cloud based on the text of the paper "Astrobiology and the Possibility of Life on Earth and Elsewhere..."

This Astrobiology Topical Team also assessed and made recommendations for the future concerning two areas in which ESA is very active.

The Earth: a research tool for astrobiology

The first set of recommendations concerns the exploration of particular regions of our own planet. Some regions, often remote and desert, present environmental conditions -- acidity, temperature, humidity, etc. -- that make them relatively good analogues of other planets of the solar system, such as Mars, or even of the primitive Earth. These extraterrestrial environments are also simulated in many laboratories. The Topical Team examined the ways in which the Earth is used for astrobiology:

organizing field trips to these analogue regions to study existing life in extreme environments: its forms, metabolisms, coping strategies, and the signatures that identify it;

searching for the oldest traces of extinct life in the oldest known rocks, and learning how these signatures are preserved over time;

exposing samples to laboratory-simulated outer-space or planetary environments to study the changes induced in minerals, molecules, and microorganisms.

The Topical Team recommended that ESA centralize and organize calls for tenders in the future to finance field campaigns focused on these planetary analogues. These could be combined with campaigns dedicated to other fields of research such as climate or environmental studies in general: scientists would benefit greatly from the multidisciplinary synergies. Better infrastructure, centralized logistics, and improved financing at the European level will be necessary to ensure the best scientific return from this research. Better linking of the operations and results of laboratory simulation facilities with these natural analogues is also recommended. Finally, data processing, archiving, and dissemination centers are also needed, including an extensive dissemination program to the general public of the ESA member countries to raise their awareness of these activities and their key outcomes.
This report and these perspectives are detailed in "Earth as tool for Astrobiology - A European Perspective" (open access here).

Tag cloud based on the text of the paper "Earth as tool for Astrobiology -- A European Perspective"

Space, a research tool for astrobiology

Beyond the popular exploration missions (exemplified by the Mars rover Curiosity and the Rosetta probe and its lander Philae), space is a privileged tool for astrobiology studies. The Topical Team focused on a comprehensive international review of the experiments conducted in Earth orbit and beyond to study the evolution of organic matter and the resistance of living organisms to the highly hostile environment of space. This environment and its unique combination of different types of radiation, solar and cosmic, is particularly difficult to simulate in the laboratory. The first experiments exposing microorganisms to these conditions date back to the Gemini and Apollo missions in the 1960s and 1970s. Supporting hardware and devices have since been significantly improved, and at present the exterior of the International Space Station is regularly used as a laboratory for conducting chemical or biological astrobiology studies in outer space. The return to Earth of space capsules is even used to simulate entries of meteorites into the atmosphere to better understand how life`s molecular building blocks could have been affected by their delivery to Earth.
The main questions addressed by these experiments are the following:

What does the resistance of microorganisms to space conditions teach us the about possibility of finding life beyond the Earth?

What can we learn from the resistant microorganisms that might be relevant to “planetary protection?” (A term referring to the goal of avoiding the export of viable terrestrial organisms to other objects in the Solar System—on Mars or Europa for example—where they might proliferate).

How has the organic chemistry that led to the origins of life on Earth been influenced by processes initiated by solar or cosmic radiation?

What can we learn from such experiments to support current and future space missions?

There are, however, critical limitations to existing space facilities. Passive exposure platforms utilized outside the International Space Station do not allow "real-time" measurements of the alteration of exposed samples, so researchers cannot analyze them until they are shipped back to Earth. Next-generation platforms should therefore allow in-situ, real-time measurements; they should also support experiments at low temperatures to better simulate cometary ices, the surface of Mars, or the environments of the icy satellites of the giant planets, such as Europa and Enceladus.
The Topical Team also recommended access to orbits more exposed to radiation than ISS-hosted facilities. Satellites in higher orbits, for example polar orbits, would offer samples an increase in charged-particle doses more representative to the conditions of interplanetary space: space craft in such "high-inclination" orbits venture beyond the radiation-shielding effects of Earth`s magnetic field. Implementation of these recommendations will likely be facilitated by the development of nanosatellites (such as those based on the Cubesat architecture). This new generation of experiments will considerably increase the scientific return of space sample-exposure experiments. The Topical Team therefore recommends that ESA seriously consider such innovative architectures.
This review and its perspectives are detailed in "Space as a Tool for Astrobiology: Review and Recommendations for Experiments in Earth Orbit and Beyond" (open access here).

Tag cloud based on the text of the paper "Space as a Tool for Astrobiology: Review and Recommendations for Experimentations in Earth Orbit and Beyond."